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  1. #1

    DA**!!! Another hole in a SL750 piston


    Hoping for some assistance here, I know this is the right place to get the info.

    I had burned a hole about a month ago in the #3 cylinder piston (closest to the fuel tank), I read about it burning first b/c a lack of fuel in the last cylinder.

    So, I put a new piston and rings in the #3 cylinder. As well as fixing the fuel pump issue, went to the Triple outlet pump. All new fuel lines & fuel filter.

    Went to the water last weekend, and did the break-in for the new rings.
    Towards the end of the day, I started running it at 3/4 throttle, it screamed, had no issues. My other SLT750 couldn't keep up even at 3/4 throttle.

    Now, I went to the water yesterday, and my buddy and my wife unloaded the skis, I told them to go slow and let them warm up for a few minutes.

    By the time I pulled the trailer around to the campsite, my buddy was sitting in the middle of the lake. I towed him to shore, and decided that I would try and figure out what it was doing. I rode it just outside the wake zone. At full throttle, it felt like it just wouldn't break plain, so I thought maybe a filed plug.

    When I came in, I took the seat off and watched the fuel go through the fuel lines, so I didn't think it was a fuel issue. I told him it's either a filed plug, or a hole in a piston.

    Wouldn't you know it!!!!!!! I now have a hole in the middle cylinder. I'm running BPR7ES plugs, are these to hot? Why in he** does it keep doing this?

    Looking for some well needed assistance, I'm about out of patience with this ski. Borderline repairing and selling!!! Help.

    Thanks in advance,

  2. #2
    those are to hot! you should run the 8's

  3. #3

    Did you mean?


    Are these BPR8ES?



  4. #4
    seaobin's Avatar
    Join Date
    Jun 2007
    Raleigh, North Carolina, United States

    they will run a hair cooler than the 7 series and help your pistons live longer

  5. #5
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    You may have a vacuum leak. Pressure test the motor. It may have been the cause of the first piston as well.

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Quote Originally Posted by beerdart View Post
    You may have a vacuum leak. Pressure test the motor. It may have been the cause of the first piston as well.
    I agree.

    Did you also replace the fuel lines, clean/inspect the petcock, and thoroughly clean the carbs?

  7. #7
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Mesa, AZ
    Very, very possible that your bore slipped down in your cylinder, just a hair (thickness of your fingernail will do it.)

    Got a picture of the piston, and/or head gasket?

  8. #8

    Yea and No

    I actually put new fuel lines from the carbs to the pump, from the pump to the separator, from the separator to the fuel selection valve.

    The fuel lines and pick-ups in the tank were new, the lines from the tank to the selection valve were in very good shape. Like they had recently been replaced.

    No, I did not clean the carbs, sure I should have. My question is what is this? Found this underneath the carbs last night while snooping around. The hose to the top looks like some sort of vacuum, but the black hose is loop around to a in and out. Seeming to bypass something. Could this be the cause of the problem?

    Please advise.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  9. #9
    seaobin's Avatar
    Join Date
    Jun 2007
    Raleigh, North Carolina, United States
    that is the autocock that we all talk about removing. get it out of there. Did you upgrade to the triple pump yet

  10. #10


    Yes I now have the triple outlet fuel pump. What does that clear, small line go to?

    Do I have to cap the other end off? Take it out completely?

    Could this have caused my hole in the pistons?

    Thanks, John

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